I/O Modules for Mobile Machine OEMs

By Andy Pagones, Quality Systems & Controls

I/O distribution modules are devices that offer many benefits to mobile machine OEMs. Also called I/O extension or expansion blocks, these robust electronic modules can radically improve a machine’s signal and power cabling distribution. Modules are available with several variations, focused on multiplexing the following signals:

  • inputs (e.g., sensor signals that feed ECU inputs)
  • outputs for driving light or heavy electrical loads
  • communication bus networking
  • pass-through wiring (“passive” modules)
  • signals interfacing to a CAN bus (“active” modules)

In general, distribution block solutions simplify conventional machine wiring. Connections are typically made using standard (M8, M12, etc.) connectors. Newer designs use sealed Deutsch connectors rated to IP67, the preferred standards choice for many. These modules are designed for ruggedness to satisfy the demands of the mobile fluid power controls market. Short-circuit and overcurrent protection are built into each connection point for automatic protection of connected circuits.

Significant reductions of overall cabling and harness lengths become possible. Especially for larger machines with sensor or actuator groupings scattered across the machine, the need for heavy “home run” cabling can be eliminated. Complete machine wiring can be designed, routed, and reconfigured very quickly due to the flexible, modular nature of the connections.

Each module can contain up to 10 connection ports, in the form of molded Deutsch receptacles. Each 4-pin port accommodates power, return, and two I/O lines. Often the I/O pairs are complementary, such as a PWM output along with its current feedback input. “Active” modules dedicate two ports to CAN wiring. “Passive” modules do not include the CAN ports. One active module dedicates its I/O ports to only inputs, for up to 16 configurable input signals. One model dedicates I/O to digital output drivers only, and a third handles a mix of configurable digital and PWM outputs. A “combo” model contains a mix of inputs and outputs, and a multi-port CAN splitter is also available. Further variants are being developed for higher total current, other bus types, popular I/O mixes, and can be configured for stand-alone controllers.

Built-in LEDs for each I/O allow quick visual diagnosis of problems. Power LEDs indicate whether each module section is properly supplied. Signal LEDs indicate activity or fault status of each I/O. Communication LEDs allow network connection monitoring. These LEDs can greatly reduce the time it takes to diagnose a wiring fault, because the abnormal LED state directly indicates the problem location. There is no longer the need to find schematics and probe harnesses using a trial-and-error measurement approach. Module diagnostic data are available and, of course, are broadcast on the CAN bus.

Programming the configuration of a module is quite straightforward using either the manufacturer’s or an industry-standard software. Graphical interfaces make it easy to optimize the I/O parameters and physical arrangement, providing an overall visualization of the signal routing.

When evaluating the investment required to change over to a distributed cabling solution, it is important to consider all the costs involved. Significant savings are available in:

  • prototyping time due to flexible reconfigurability and reusability
  • product assembly labor
  • initial debug and machine final test times
  • ECO and harness rework labor
  • scrap material waste
  • service diagnostics and troubleshooting time

The equation that computes total cost is not as trivial as simply comparing materials’ costs. However, the ability to reduce wiring length and weight, to gain significant diagnostic knowledge of the entire electrical system, and to reduce time spent on wiring and troubleshooting all represent significant savings opportunities that cannot be ignored.